"I'm marrying my best friend," she told PEOPLE on Saturday following West's concert at the MGM Grand in Las Vegas.

Kardashian said the engagement came as a shock. "It was a complete surprise. I had no idea. I was shaking the entire time – like, is this really happening? It was an out-of-body experience," she said.

And while Kardashian, 33, and West, 36, have barely had time to even start thinking about planning a wedding, there is one decision that is already made: She says stepdad Bruce Jenner, who recently separated from her mom Kris, will be the one walking her down the aisle.

"Of course he will. [Kanye and I] honestly haven't had a moment to talk about [the wedding] or even breathe, but whatever he wants!" she said.